Taxonomic studies on the genus Isotrema (Aristolochiaceae) from China: II. I. brevilimbum (Aristolochiaceae), a new species from Guizhou, China

Abstract A new species of Isotrema was recently discovered from Guizhou, China and is here named as I. brevilimbum. It is most similar to I. ovatifolium and I. wardianum, but differs in the morphology of leaves and flowers. A detailed description for the new species, along with line drawings, photographs, as well as morphological comparisons with similar species, are provided. In addition, the distribution of I. wardianum in China is here confirmed.

Phenology. Flowering from May to August, fruiting from July to September. Etymology. The specific epithet refers to the short cylinder perianth limb of the new species. The "brevi" means "short", "limbum" means "limb", so the new species is named Isotrema brevilimbum.
Distribution and habitat. The new species is currently only known from Weining County of Guizhou, China. It grows by the roadside of farmland at an altitude of ca. 2200 m.
Preliminary conservation status. Isotrema brevilimbum is known from a single population including two individuals on the roadside of farmland. The new species is assigned a preliminary status of vulnerable (VU) according to the IUCN Red List Categories (IUCN 2012). However, since very few details exist about its natural distribution, the lack of sufficient data currently does not allow a final risk evaluation and the species might be regarded as data deficient (DD). Further field surveys in western Guizhou and northeastern Yunnan are needed to gain more information on its distri-bution. Not only is the area not under protection as a nature reserve, but also habitat disturbance brought about by human activities, such as grazing and farming, may have a negative impact on the new species.
Note. Isotrema wardianum was previously only known from Myanmar and India. Sun and Zhou (2002) later reported the species from China, according to a specimen collected from Medog County of Tibet (H. Sun et al. 4935), but without flower or fruit. Nevertheless, the species had long been neglected by taxonomic studies of Huang et al. (2003), Do et al. (2015a), and Zhu et al. (2019a, 2019d on Chinese Isotrema. It was not until 2018 that we discovered a seedling of Isotrema sp. at the same locality as that of H. Sun et al. 4935 and transplanted it in the nursery of the Kunming Institute of Botany. A year later, the plant grown from this seedling bloomed and enabled us to identify it as I. wardianum (Figs 2G-I, 4G-I) and confirm its distribution in China.

Discussion
Isotrema brevilimbum is morphologically similar to I. ovatifolium and I. wardianum in the shape, size, and color of flower and the dark-purple papillae in the inner surface of perianth limb, but they can be distinguished by the morphology of lamina, the angle between perianth limb and upper tube, as well as the length and mouth of limb. Detailed morphological comparisons among the three species are summarized in Table 1   These characters were based on field observation, related specimens and literatures (Hwang 1981;Ma 1989a;Huang et al. 2003